In emerging digital applications and especially in new generations of Set-Top-Boxes or Digital Television Sets, the presence of more than one digital front-ends enables new services to the end-customer. In particular, viewing one program while recording another one on a digital media is a very strong demand from end-customers, since that functionality was natural in the analogue world, with a TV set together with a VCR (Video Cassette Recorder).
This implies that the digital system be able to process two different transport streams, coming from the two digital front-ends. The immediate answer to that is to implement two demultiplexers in the system.
Now, most of the digital MPEG decoders today only support one transport stream input and demultiplexing.